Add support for XLS-81 Permissioned DEX (#5404)

Modified transactions:
- OfferCreate
- Payment

Modified RPCs:
- book_changes
- subscribe
- book_offers
- ripple_path_find
- path_find

Spec: https://github.com/XRPLF/XRPL-Standards/pull/281

src/libxrpl/protocol/InnerObjectFormats.cpp

@@ -165,6 +165,13 @@ InnerObjectFormats::InnerObjectFormats()
          {sfSigningPubKey, soeOPTIONAL},
          {sfTxnSignature, soeOPTIONAL},
          {sfSigners, soeOPTIONAL}});
+
+    add(sfBook.jsonName,
+        sfBook.getCode(),
+        {
+            {sfBookDirectory, soeREQUIRED},
+            {sfBookNode, soeREQUIRED},
+        });
 }
 
 InnerObjectFormats const&